No abstract

Based on the amino acid sequence YPFV found in the soy -conglycinin -subunit, which is common to an opioid peptide human -casomorphin-4, peptides YPF-VV, YPFVVN, and YPFVVNA were synthesized according to their primary structure. On guinea pig ileum (GPI) assay, they showed opioid activity (IC 50 = 6.0, 9.2 and 13 M respectively) more potent than humancasomorphins, and were named soymorphins-5, -6, and -7, respectively. Their opioid activities on mouse vas deferens (MVD) assay were less potent than on GPI assay, suggesting that they are selective for the opioid receptor. Human -casomorphin-4 and soymorphin-5 were released from the soy 7S fraction (-conglycinin) by the action of gastrointestinal proteases. Soymorphins-5, -6, and -7 had anxiolytic activities after oral administration at doses of 10-30 mg/kg in the elevated plus-maze test in mice.Key words: opioid peptide; opioid receptor; anxiolytic effect; soy protein; -conglycinin -subunitOpioid is a chemical substance that has morphine-like action. An opioid peptide, bovine -casomorphin-7 (YPFPGPI), isolated from casein peptone, was the first example of bioactive peptides released from food proteins.1) We have reported that human -casomorphin-4 (YPFV) and related peptides derived from human -casein also have opioid activities, though they are less potent than their bovine counterparts.2) Of three soyconglycinin subunits (, 0 , and ), 3) the -subunit has the human -casomorphin-4 sequence (YPFV). Longer peptides, YPFVV, YPFVVN, and YPFVVNA, were synthesized according to the primary structure of theconglycinin -subunit by the Fmoc strategy, and their opioid activities were tested by guinea pig ileum (GPI) and mouse vas deferens (MVD) assay, as previously described.4) All experiments were approved by the Kyoto University Ethics Committee for Animal Research Use.The peptides were found to have opioid activities on GPI assay. Figure 1 indicates the typical suppressive effect of YPFVV on electrically stimulated contractions on GPI assay. YPFVVN and YPFVVNA also dosedependently inhibited ileum contractions (data not shown). These results suggest that YPFVV, YPFVVN, and YPFVVNA have opioid activities; they were named soymorphins-5, -6, and -7 respectively. The opioid activities of synthetic peptides derived from the soyconglycinin -subunit are summarized in Table 1. The IC 50 values of soymorphins-5, -6, and -7 on GPI assay were 6.0, 9.2, and 13 mM respectively, and their opioid activities were more potent than those of humancasomorphin-4, -5, and -6 (IC 50 = 20, 14, and 25 mM, respectively). There are three types of opioid receptors: , , and . 5,6) The opioid activities of soymorphins were larger on GPI assay than those on MVD assay, suggesting that these peptides are selective for theopioid receptor. The affinities for the -opioid receptor were 17, 39, and 47 mM respectively, and the rank order of their affinities for the receptor was consistent with that of the opioid activities on GPI assay. Taking all this 1 µM 3 µM 10 µM 1 min Guinea Pig Ileum (GPI) Assay. Ileum-...